NORTH INDIAN OCEAN 93 



February in the frequency of high waves of either category, the east- 

 tropical smooth area, as defined on the charts by the contours for 

 "low" in 60 percent frequency, extends tongue-like, something like 

 1,800 miles farther out along the equator from the American coast in 

 northern winter than in northern summer for seas, and apparently 

 as far as the longitude of the Marquesas and of the Paumotos (about 

 long. 140° W.) for swells, to judge from such scattered information 

 as is at hand. And a corresponding expansion of the equatorial- 

 American region, where swells and seas alike are low for more than 

 80 percent of the time, takes place from northern summer to winter. 



Ships crossing the northwestern part of the South Pacific in north- 

 ern winter, or in early spring, must however take account of the pos- 

 sibility that they may encounter the dangerous seas that are generated 

 by tropical hurricanes, for these develop most often there from De- 

 cember to March. Such of these storms as originate in the Coral Sea 

 usually move either toward New Caledonia, or past New Guinea, or — 

 more rarely — southward paralleling Australia; others of great sever- 

 ity occur from time to time in the neighborhood of the Fijian and 

 Samoan Island groups. 



NORTH INDIAN OCEAN 



Summer. — The chief causes for high seas in the Indian Ocean north 

 of the equator are the winds of the Southwest Monsoon, which blow 

 strongest, and with frequent squalls and gales, from June through 

 August. High seas, therefore, are the most frequent there in summer 

 or just when they are least so in the northern parts of the Atlantic 

 and of the Pacific. Regional differences in the frequency with which 

 a high sea is to be expected during the monsoon season (pi. XVII) are 

 also clearly governed by the prevailing strength of the wind. Thus 

 the region in the Bay of Bengal where 8-foot seas, and higher, are 

 reported during more than one-tenth of the time during July and 

 August, corresponds closely with that where the summer monsoon 

 averages stronger than 16 miles per hour. And the limits between 

 India, Arabia, and Africa, within which a high sea has been reported 

 in frequencies greater than 20 percent, and than 40 percent, for July 

 and August combined, coincide almost exactly with those within 

 which the monsoon averages stronger than 16 and 20 miles per hour, 

 respectively, and where gales of force 7, or stronger, are then the most 

 frequent. High seas, indeed, are reported locally in frequencies about 

 as great (maximum 74 percent) within this general region, during 

 the monsoon season, as they are anywhere in the world ; and they rise 

 there to heights of 20 feet or more during about 10 percent of the time 

 (table 8, p. 21). Corresponding to this, we read of the western coasts 

 of Hindustan that all small craft near Bombay are laid up from the 



